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Abstract: 3-D Seismic Delineation and Geologic Explanation of Channelization in the Frio Formation of Javelina/East McCook Field, Hidalgo County, Texas

John L. Gibson

Sinuous, channel-form features were recognized on seismic amplitude time-slice maps of the shallow Oligocene Frio Formation on several Shell proprietary 3-D seismic surveys in west-central Hidalgo County, Texas. A case study of channel morphologies observed in the Frio Formation within the 50 mi2 3-D seismic survey over Javelina/East McCook field was undertaken to better understand the distribution, lithology, origin, and hydrocarbon potential of these features.

Ten separate channel-like amplitude features are observed in flattened time slices within a 200 m (approximately 1100 ft) interval on 3-D seismic. The channels have various azimuthal orientations and varying degrees of sinuosity. Several of the features have lengths that span the 3-D survey area (10 mi); apparent

channel widths range from 200 to 2000 ft. The channelized seismic events tie to an interval of interbedded mudstones and claystones with siltstones. Two of the channels seen on seismic, and which were penetrated by wells, correlate to siltstone and mudstone intervals that have gross thicknesses of 30 to 60 ft. The lithologies and dimensions of the two channels indicate that they are probably small mudstone/siltstone-filled tributary/distributary channels deposited in a coastal floodplain environment; a comparison of the apparent channel dimensions to the dimensions of small channels/bayous of the modern-day Texas Gulf Coast supports this interpretation.

Correlation of wells adjacent to the channels indicates that sandy point-bar facies are not present in association with the channel fill, which discounts the idea that high-quality reservoirs are flanking these particular mud-filled channels.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994